@anamur-- That's a good question. I'm not an expert, and I think you should talk with your physician about this.
The only thing I've heard about, that is said to contribute to myocardial fibrosis, is medications and supplements used to treat conditions like depression, especially 5-Hydroxytryptophan supplementation.
5-Hydroxytryptophan is a chemical that increases serotonin production. Serotonin is the "feel good" hormone that our body produces naturally. It is known to be too low in individuals who suffer from depression and they are sometimes prescribed 5-Hydroxytryptophan to help boost it.
Some doctors think that since this chemical can also be metabolized in the heart, it can lead to heart tissue scarring or make myocardial fibrosis worse if it exists.
I also have chronic heart disease and myocardial fibrosis in my family. I've been trying to read up on it to understand how it works, but it's a complicated condition and it appears that there is more than one cause. From what I've read though, I don't think it's genetic.